In the context of the present invention super-hard materials are defined as those materials having a Vickers hardness of no less than 2000 kg/mm2. These materials include a range of diamond materials, cubic boron nitride materials (cBN), sapphire, and composites comprising the aforementioned materials. For example, diamond materials include chemical vapour deposited (CVD) single crystal and polycrystalline synthetic diamond materials of a variety of grades, high pressure high temperature (HPHT) synthetic diamond materials of a variety of grades, natural diamond material, and diamond composite materials such as polycrystalline diamond which includes a metal binder phase (PCD) or silicon cemented diamond (ScD) which includes a silicon/silicon carbide binder phase.
In relation to the above, it should be noted that while super-hard materials are exceeding hard, they are generally very brittle and have low toughness. As such, these materials are notoriously difficult to cut. Any cutting method must be sufficiently aggressive to overcome the extreme hardness of the material to form a cut while at the same time must not impart a large degree of stress or thermal shock to the material which would cause macroscopic fracturing of the material due to its brittle nature and low toughness. As such, there is narrow operating window for achieving successful cutting of super-hard materials and many available cutting methods fall outside this operating window. For example, most cutting methods are not sufficiently aggressive to cut super-hard materials to any significant extent in reasonable time-frames. Conversely, more aggressive cutting techniques tend to impart too much stress and/or thermal shock to the super-hard material thus causing cracking and material failure. Furthermore, certain cutting methods have operational parameters which can be altered so as to move from a regime in which no significant cutting of a super-hard material is achieved into a regime in which cutting is achieved but with associated cracking and failure of the super-hard material. In this case, there may or may not be a transitional window of parameter space in which cutting can be achieved without cracking and failure of the super-hard material. The ability to operate within a suitable window of parameter space in which cutting can be achieved without cracking and failure of the super-hard material will depending on the cutting technique, the size of any transitional operating window for such a technique, and the level of operation parameter control which is possible to maintain cutting within the window of parameter space in which cutting can be achieved without cracking and failure of the super-hard material.
In light of the above, it will be appreciated that cutting of super-hard materials is not a simple process and although a significant body of research has been aimed at addressing this problem current cutting methods are still relatively time consuming and expensive, with cutting costs accounting for a significant proportion of the production costs of super-hard material products.
Super-hard materials are currently cut with one or more of:                (i) wire EDM (Electrical Discharge Machining) machines for electrically conducting materials such as doped CVD synthetic diamond, HPHT synthetic diamond, and cBN products;        (ii) high power lasers for electrically insulating materials such as un-doped CVD synthetic diamond, HPHT synthetic diamond and cBN products; or        (iii) cutting saws typically impregnated with other super-hard materials such as diamond.        
EDM cutting is efficient for electrically conductive materials, however cannot be used on any insulating materials. Traditional saws can be used for providing small cuts, but become time and cost inefficient when used for bulk processing, as well as struggling to provide good cuts at high depths. To obtain efficient cutting with lasers, the beams need to be focused to a small, very intense spot. Whilst a focused beam is very suitable for relatively thin products, the kerf losses, due to the fact the beam is divergent, having been focused down from a relatively large starting beam, result in a high amount of material wastage and increased laser cutting time. This is particularly problematic when cutting vertically through thick layers of super-hard material or cutting laterally through a large area layer of super-hard material such as when large wafers of CVD synthetic diamond or slugs of cBN need to be sliced into relatively thin wafers.
The need for methods which are capable of processing larger pieces of super-hard material has increased in recent years as synthesis technologies have been developing to allow fabrication of larger pieces of super-hard material. For example, in recent years techniques have been developed for growing layers of single crystal CVD diamond over larger areas using chemical vapour deposition techniques. In such a technique, a plurality of smaller single crystal substrates may be tiled together into an array and then a coherent single layer of single crystal CVD diamond material can be grown over the tiled array of substrates. One problem with such a fabrication technique is that it is difficult to then remove the large area layer of single crystal CVD diamond material from the tiled array of substrates on which it is grown. While the previously described cutting techniques, such as a focused high power laser, can be used to slice a small crystal of diamond material from its associated growth substrate, such a technique is not suitable for removal of a large area layer of single crystal material from a tiled array of substrates as the process requires a very deep cut to horizontally slice the large area layer of material from its associated growth substrate. Accordingly, to date such large area layers of super-hard material have been removed from the substrate on which they are grown using a chemical etch and lift-off technique. Such a technique is described in GB2488498 and comprises: implanting ions into a plurality of single-crystal diamond substrates to form non-diamond layers in the vicinity of the surfaces of the single-crystal diamond substrates; arranging the single-crystal diamond substrates to form a mosaic pattern on a flat support; growing a single-crystal CVD diamond layer on the ion-implanted surfaces of the single-crystal diamond substrates; and etching the non-diamond layers to separate the single-crystal CVD diamond layer from the plurality of single-crystal diamond substrates.
Such implantation, growth, chemical etching, and lift-off techniques have several associated problems. For example, the implantation technique can damage the growth surface of the substrates such that the CVD material grown thereon is of poorer quality. Furthermore, the etching step can be difficult to control and can be time consuming and expensive.
It is an aim of embodiments of the present invention to solve one or more of the aforementioned problems.